In general, inkjet printing machines or printers include at least one printhead unit that ejects drops of liquid ink onto an imaging receiving member. The printhead units include one or more printheads that operate a plurality of inkjets that eject liquid ink onto the image receiving member. The ink can be stored in reservoirs located within cartridges installed in the printer.
Different types of ink can be used in inkjet printers such as an aqueous ink or an ink emulsion. In one type of inkjet printer, ink is supplied in a gel form. The gel is heated to a predetermined temperature to change the viscosity of the ink so the ink is suitable for ejection by a printhead. Other inkjet printers receive ink in a solid form, i.e. phase change ink, and then melt the solid ink to generate liquid ink for ejection onto the image receiving member. Phase change inks remain in a solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. Once the ejected ink is deposited on an image receiving member, the ink droplets solidify. The solid ink is typically placed in an ink loader and delivered through a feed chute or channel to a melting device that melts the ink. The melted ink is then collected in a reservoir and supplied to one or more printheads through a conduit or the like.
An inkjet printer can include one or more printheads. Each printhead contains an array of individual nozzles for ejecting drops of ink across an open gap to the image receiving member to form an image. The area adjacent the printhead or printheads where ink can be deposited is generally known as a print zone. The image receiving member can be a continuous web of recording media, one or more media sheets, or a rotating surface, such as a print drum or endless belt. Images printed on a rotating surface are later transferred to recording media, either continuous or sheet, by a mechanical force in a transfix nip formed by the rotating surface and a transfix roller.
In an inkjet printhead, individual piezoelectric, thermal, or acoustic actuators generate mechanical forces that expel ink through an orifice from an ink filled conduit in response to an electrical voltage signal, sometimes called a firing signal. The firing signal is generated by a printhead controller in accordance with image data. An inkjet printer forms a printed image in accordance with the image data by printing a pattern of individual ink drops at particular locations on the image receiving member. The locations where the ink drops land are sometimes called “ink drop locations,” “ink drop positions,” or “pixels.” Thus, a printing operation can be viewed as the placement of ink drops on an image receiving member in accordance with image data.
Various printing systems can include a moving belt that carries one or more sheets of print media through a predetermined path while images are formed on the media sheets. An example of such a device is an inkjet printer that includes a moving belt. The moving belt carries one or more media sheets past one or more marking stations. Each marking station can include at least one printhead that ejects ink drops onto the media sheets as the sheets move through the print zone. The marking stations can be located at different positions along the path of the belt. In some embodiments, each marking station is configured to eject ink having a single color. Each marking station forms a portion of a color image using one ink color on each media sheet, and the arrangement of the different colored drops of ink from the marking stations forms a full-color image on the media sheets. One common example of such a printing system forms images using a combination of inks having cyan, magenta, yellow, and black (CMYK) colors.
When using a moving belt, inkjet printers can use a sheet holddown device to insure the sheets remain stable and fixed to the belt during printing. Some printers incorporate a vacuum source that is operatively connected to a vacuum platen to hold the sheets in place. The vacuum platen includes a plurality of passageways or ports to enable air to be drawn through the platen towards the vacuum source. The vacuum platen is located adjacent to the back side of the belt as the belt moves the print media by the marking stations. The belt may include a plurality of apertures or holes to enable the vacuum source to exert a negative pressure on the media sheets through the belt. Thus, the air being pulled through the platen pulls the media against the belt to help maintain the position of the media while being printed. Other embodiments can include an electrostatic member positioned adjacent to the belt that generates an electrical charge to counteract an electrical charge on the media sheets, thereby attracting the media sheets to the moving belt. Still other embodiments can include mechanical members, such as gripper bars or hold-down rollers that push the media sheets against the moving belt, and consequently push the moving belt against a support member, such as a backer roller, positioned on the back side of the moving belt to hold the media sheets in place.